Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for deghosting wave-fields belonging to different vintages collected at various times.
Discussion of the Background
Seismic data acquisition and processing generate a profile (image) of the geophysical structure (subsurface) underground. While this profile does not provide an accurate location for oil and gas, it suggests, to those trained in the field, the presence or absence of oil and/or gas. Thus, providing a high-resolution image of the subsurface is an ongoing process for the exploration of natural resources, including, among others, oil and/or gas.
Recently, so-called 4-dimensional (4D) or time-lapse surveys have become an important addition to the product offerings of seismic survey companies. In 4D surveys, a first survey (baseline) taken at a first time operates as a baseline to indicate the potential presence/absence of hydrocarbon deposits in a given area. A second survey (monitor), taken later in time (months or years), operates to indicate the change in hydrocarbon deposits in the same geographical area, e.g., after removal of the hydrocarbons has occurred. By comparing the two surveys, a 4D picture (where time is the fourth dimension) can be developed which can be used for a number of purposes, e.g., to determine the continued viability of a hydrocarbon field, where to drill, when to inject a liquid to stimulate production, well management, etc. However, in order for a 4D survey to be accurate, the first and second surveys need to be performed in a very similar manner, e.g., shot position, receiver position, etc. This gives rise to a need to make surveys highly repeatable and to determine when subsequent surveys are not accurate repetitions of an earlier, baseline survey.
However, the earlier seismic surveys located the seismic receivers at a same depth, thus not being able to achieve broadband data. The more recent seismic surveys place the seismic receivers at variable and/or deeper depths, resulting in a broadband data acquisition.
Broadband processing that involves receiver deghosting (Özdemir et al., 2008; Riyanti et al., 2008; Poole, 2013; Wang et al., 2014), shot deghosting/designature (Van der Schans and Ziolkowski, 1983; Poole et al., 2013; Wang et al., 2015), and broadband surveys (Carlson et al., 2007; Robertsson et al., 2008; Soubaras, 2010) have been widely accepted as methods for extending the bandwidth of marine seismic data. Two questions have been frequently raised in the context of 4D time-lapse processing: (1) is it possible to obtain deghosted 4D signals for broader bandwidth monitors and conventional baselines, and (2) is it possible to apply 4D processing between conventional surveys and broadband surveys? In an attempt to answer both questions, Hicks et al. (2014) demonstrated that deghosting was possible and important for 4D processing of multiple vintages with different receiver-depth profiles using a 2D ghost-wavefield elimination algorithm (Poole, 2013).
Wang et al. (2014) proposed using a progressive sparse Tau-P inversion algorithm for 3D deghosting of single-component marine seismic data. This algorithm was used to deghost both baseline and monitor data sets separately in 4D processing. However, this algorithm does not take advantage of the potentially better spatial sampling from different surveys and better overall signal-to-noise (S/N) due to complementary ghost-notch frequencies (if receiver depths of two or more vintages are different).
Thus, there is a need to process traditional and new vintages, which have different frequency content and/or recording position, in a more advantageous way. Accordingly, it would be desirable to provide systems and methods with such capabilities.